1. Field of the Invention
The present invention relates to the structure of contacts of a so-called tandem sliding switch having a first and a second movable contact which respectively slide on a first and a second group of fixed contacts.
2. Description of the Related Art
A conventional arrangement of the structure of contacts of a sliding switch of this type is shown in FIGS. 40 and 41. This switch is used for, for instance, a window regulator for vertically moving the window glass of an automobile.
In FIG. 40, a first group 2 of fixed contacts and a second group 3 of fixed contacts are arranged in parallel on a substrate 1.
The first group 2 of fixed contacts comprises a first common fixed contact 2a connected to a reversible motor 4, a first positive fixed contact 2b connected to a positive terminal of a power source, and a first negative fixed contact 2c connected to a negative terminal of the power source via a ground connection.
Meanwhile, in the same way as the first group 2 of fixed contacts, the second group 3 of fixed contacts comprises a second common fixed contact 3a connected to the motor 4, a second positive fixed contact 3b connected to the positive terminal of the power source, and a second negative fixed contact 3c connected to the negative terminal of the power source via a ground connection.
A first movable contact 5 which slides on the first group 2 of fixed contacts and a second movable contact 6 which slides on the second group 3 of fixed contacts are mounted on an unillustrated contact holder. These first and second movable contacts 5, 6 are adapted to slidingly move simultaneously in the direction of arrow A in FIG. 40 and in an opposite direction thereto.
In this arrangement, in a state in which the first and second movable contacts 5, 6 are located at a neutral position indicated by two-dotted dash lines in FIG. 40, contact portions 5a, 5b of the first movable contact 5 are respectively in contact with the first common fixed contact 2a and the first negative fixed contact 2c, while contact portions 6a, 6b of the second movable contact 6 are respectively in contact with the second common fixed contact 3a and the second negative fixed contact 3c. In this state, the motor 4 is in a deenergized state and is in a neutral state.
When, upon operation of the switch, the first and second movable contacts 5, 6 slide in the direction of arrow A from the aforementioned neutral position and reach the first operating position (see the dotted dash lines in FIG. 41), the contact portions 5a, 5b of the first movable contact 5 respectively remain in contact with the first common fixed contact 2a and the first negative fixed contact 2c, but the contact portions 6a, 6b of the second movable contact 6 are changed over to a state in which they are brought into contact with the second common fixed contact 3a and the second positive fixed contact 3b.
In this state, electric current flows across the motor 4 in the direction of arrow B in FIG. 41, and the motor 4 is thereby rotated forwardly, which in turn causes the window glass to be raised and set in a raised state.
On the other hand, when, upon operation of the switch, the first and second movable contacts 5, 6 slide in the opposite direction to that of arrow A from the neutral position in FIG. 40 and reach the second operating position (see the broken lines in FIG. 41), the contact portions 6a, 6b of the second movable contact 6 respectively remain in contact with the second common fixed contact 3a and the second negative fixed contact 3c, but the contact portions 5a, 5b of the first movable contact 5 are changed over to a state in which they are brought into contact with the first common fixed contact 2a and the first positive fixed contact 2b.
In this state, electric current flows across the motor 4 in the opposite direction that of arrow B, and the motor 4 is thereby rotated reversely, which in turn causes the window glass to be lowered and set in a lowered state.
It should be noted that if the switch operation is canceled, the first and second movable contacts 5, 6 are automatically reset to the neutral position.
In the switch having the above-described arrangement, when the first and second movable contacts 5, 6 slide between the neutral position and the first operating position (during a changeover between the neutral state and the raised state), an arc occurs solely between the contact portion 6a of the second movable contact 6 and the second positive fixed contact 3b. On the other hand, when the first and second movable contacts 5, 6 slide between the neutral position and the second operating position (during a changeover between the neutral state and the lowered state), an arc occurs solely between the contact portion 5a of the first movable contact 5 and the first positive fixed contact 2b.
For this reason, there has been a drawback in that, owing to metal powders produced by arcs, the insulation performance declines in an insulation space portion 7 between the second positive fixed contact 3b and the second common fixed contact 3a and in an insulation space portion 8 between the first positive fixed contact 2b and the first common fixed contact 2a. In other words, the insulation performance declines between fixed contacts of different polarities, respectively.